A less fussy version: mix any yoghurt and any hard cereal like Grapenuts. If you want fruit, get pre-fruited yoghurt.
My dad, blue-collar, single father, used to make this for his breakfast before work. It’s simple, fast, cheap, as sweet as you prefer, reasonably available in food deserts, and holds up well over time if you can’t eat it immediately (it gets soggy more slowly).
If you have money and want to get precious about it, you can use hand-mixed granola and skyr, but all you really need is Grapenuts and yoghurt.